The main problem encountered in endodontics during root canal treatment is being able to reach as accurately as possible the apical foramen of the root without perforating it. It is thus necessary to be able to measure the length of the root canals. Several methods exist for this purpose.
The best known and most widespread method is the tactile approach. The practitioner evaluates the length of the root canal as he gradually inserts his file into the canal. This manual technique does not require any special tools but relies entirely upon the dexterity of the practitioner.
Another method consists in taking X-rays of the tooth requiring treatment. By analysing the X-ray, the practitioner can judge the geometry of the root canals and identify the position of the apical foramen. It is, however, not unusual for the position of the apex revealed by the X-ray not to coincide with the position of the anatomical apical foramen, hence the risk of X-ray interpretation errors.
Finally, there is a third method which relies upon electronic apex locators. Used in endodontics since the end of the nineteen sixties, these apparatus rely on the principle according to which the electrical features of a human root canal are identical from one person to another. These electronic apex locator devices can be classed in three categories according to the nature of the electrical parameter that is measured.
A first category of these apparatus operates in accordance with the principle of resistance measurement. In fact, in 1962, it was demonstrated that the electrical resistance of a human root canal might reach 6.5Ω. Thus, a constant electrical resistance of 6.5Ω is obtained between a first electrode connected to an endodontic file at the moment that the latter reaches the anatomical apex and a second electrode connected to an oral mucosa.
A second category of apex locator apparatus operates in accordance with the principle of impedance measurement. In fact, it was observed that the root canal developed impedance caused by the presence of hyper-mineralised dentine along the canal, with this impedance increasing all the way along the root canal to reach a maximum at the apical constriction. As soon as the ligament is touched, the impedance drops, which can be electronically detected.
A third category of apex locator apparatus operates in accordance with the principle of frequency measurement. These apparatus measure the impedance of the dentine of the root canal by using two different frequencies and calculate the resulting impedance ratio. At the coronary part of the tooth, the impedance resulting from the two applied frequencies do not vary much, such that their ratio tends towards 1. At the apical part of the tooth, the difference in impedance between the two frequencies increases to reach its maximum value at the cemento-dentinal junction. The ratio tends towards zero at that place.
Whether the apex locator apparatus relies on measuring a resistance, impedance or frequency, an electrical connection has to be established between the apparatus and the practitioner's tool on the one hand, and between the patient and said apparatus on the other hand. This wiring is shown schematically in FIG. 1 annexed to this patent application, which shows an apex locator system based on the resistance measurement principle. Designated as a whole by the reference numeral 1, this system includes an apex locator apparatus 2, which can operate in accordance with any of the three methods for detecting the tooth apex position (resistance, impedance or frequency) and which is connected to an endodontic file 4 via an electrode 6 and to a contact terminal 8 via an electrode 10. The contact terminal 8 is hook shaped so as to be able to be hooked, for example, to the patient's lip 9. It goes without saying that endodontic file 4 could be replaced by a contra-angle if the practitioner is performing a mechanised and not a manual operation. There are thus two wires that pass from the resistance measuring apparatus: one that connects the apparatus to the file or contra-angle and the other that connects the apparatus to the patient. The presence of these two wires can be inconvenient for the practitioner whose movements are limited and who is liable to become caught in one of the wires. In order to overcome this problem, it has already been proposed to fit the contra-angle with means securing the wire that connects the latter to the apex locator apparatus. However, in that case, the practitioner is obliged to purchase a contra-angle solely for endodontic use, which is expensive.
It is an object of the present invention to overcome the aforementioned drawbacks, in addition to others, by providing an apex locator apparatus accessory that limits the inconvenience caused by the electrical connecting wires.